Cortland, If you were responding to my post re signals that don't leave the silicon, note that I pointed out that there is, at least in some cases, an output of the internal PLL which is not the advertised processor speed, but probably twice that, which is *only* used to generate the processor clock. In other words, your 1 GHz processor may have an internal PLL output of 2 GHz. [I'm basing all this on knowledge of one specific family of CPUs; others may not have this feature.] The only way you might know the actual PLL frequency is to dig into the hardware spec. of the device; many of the board designers won't know or care about this.
I certainly agree that the processor clock itself is EMC important since that's what is driving all the internal bus switching and it's practically guaranteed that the harmonics will leak out onto the board etch (on bus lines & even the power & ground planes as common mode). Although, this hidden PLL output is certainly "used" per the FCC definition, I seriously doubt you will find any evidence of it with your receiver. I never have. Regardless, I do NOT recommend playing "games" with the rules. Regards, Jack -----Original Message----- From: Cortland Richmond [mailto:72146....@compuserve.com] Sent: Saturday, August 04, 2001 6:40 PM To: ieee pstc list Subject: Re: FCC - radiated emission up to 10th harmonic During a previous life (heh!) we had applications for FCC grants returned without action because we had applied not for the on-chip frequency, but only for the distributed clock. Actually, testing will show that is the correct approach. A 1 GHz processor can radiate enough that a 66 MHz clock is certainly not the only thing you have to worry about. Cortland ------------------------------------------- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson: pstc_ad...@garretson.org Dave Heald davehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://www.rcic.com/ click on "Virtual Conference Hall," ------------------------------------------- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson: pstc_ad...@garretson.org Dave Heald davehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://www.rcic.com/ click on "Virtual Conference Hall,"
